Examples of conventional memory devices that read and write information using multiple probes include such devices as those disclosed in J. Sliwa, Jr., Microvibratory Memory Device, U.S. Pat. No. 5,216,631 ("Sliwa, Jr."). In such devices, techniques for controlling the spacing between needles and the surfaces of detected objects in STM (scanning tunnel microscopes), and in AFM (atomic force microscopes) operated in a non-contact mode, are used to control the spacing between the tip of a tapered needle and a memory medium in a cell of a memory device. To read and write information in such memory devices requires that the distance between the memory medium and the tip of the needle be dynamically adjusted to a precise value. This distance adjustment is accomplished by detecting the distance between the memory medium and the tip of the needle.
In the memory devices disclosed by Sliwa, Jr., the distance between the memory medium and the tip of the needle is detected by measuring a tunneling current or by measuring a force between the tip of the needle and the memory medium. Accordingly, in such memory devices, a detection circuit, and a signal processing circuit for performing distance detection and distance control must be provided for each probe, in addition to a W/R circuit. These additional circuits, i.e., the detection circuits and signal processing circuits, cause an overall increase in the surface area occupied by each probe and its associated circuits. As a result, when the probes and their associated circuits are located on the same substrate, the detection and signal processing circuits make it more difficult to achieve a high probe density.
For the above reasons, in the memory devices disclosed by Sliwa, Jr., the W/R circuits, detection circuits, and signal processing circuits are located on a different substrate from the substrate in which the probes are formed. Separate manufacturing processes are used to form the probes and their associated circuits in separate locations.
As a result of the probes and their associated circuits being located on different substrates in the memory devices disclosed by Sliwa, Jr., the probes are connected to their associated circuits by relatively long wiring. The relatively long wiring has considerable stray capacitance, and easily picks up noise. To ameliorate the effects of stray capacitance and noise pickup in the interconnections between the probes and their associated W/R circuits necessitates an increase in the bit size of the memory medium.
Moreover, the distance between the probes and their associated circuits varies from probe to probe. This creates a skew in the probe locations so that a high parallelness cannot be obtained between the probes. This leads to problems. For example, the electrical characteristics of the areas between the probes and their associated circuits may differ. As a result, performance values which are important in a memory device, e.g., data transmission rate, assurance of redundancy, and error correction functions, are impaired.
In memory devices that use multiple probes to read and write information, the amount of information that is read or written in one access operation increases with increasing probe density. In the wiring used to transmit the reading or writing signals, at least one line is required for each probe. Consequently, the large number of lines required interferes with achieving a high probe density.